Computing devices and other similar devices implemented to send and/or receive data can be interconnected in a wired network or a wireless network to allow the data to be communicated between the devices. Wired networks, such as wide area networks (WANs) and local area networks (LANs) for example, tend to have a high bandwidth and can therefore be configured to communicate digital data at high data rates. One obvious drawback to wired networks is that the range of movement of a device is constrained since the device needs to be physically connected to the network for data exchange. For example, a user of a portable computing device will need to remain near to a wired network junction to stay connected to the wired network.
An alternative to wired networks is a wireless network that is configured to support similar data communications in a more accommodating manner. For example, the user of the portable computing device can move around within a region that is supported by the wireless network without having to be physically connected to the network. A limitation of wireless networks, however, is their relatively low bandwidth which results in a much slower exchange of data than a wired network. Wireless networks will become more popular as data exchange rates arc improved and as a coverage area supported by a wireless network is expanded.
Monopole and dipole antennas can be implemented in broadcast and communication applications. For a vertically polarized antenna, an E-plane contains an electric field vector and coincides with a vertical plane relative to the antenna. An H-plane contains a magnetic field vector and coincides with a horizontal plane relative to the antenna. The antenna radiates an omni-directional transmission pattern in the H-plane. That is, an electromagnetic field is radiated in an omni-direction pattern from the antenna in a plane that is normal (e.g., S perpendicular) to an axis of the antenna.
An antenna described as “omni-directional” implies an antenna that radiates equally in all directions. However, although some antennas are identified by their manufacturers as “omni-directional”, an actual omni-directional antenna has not been devised. For a horizontally polarized antenna, the transmission pattern in the E-plane is not truly omni-directional. That is, the electric field radiated in a plane that is perpendicular to the axis of the antenna is not a complete omni-directional transmission pattern.
A conventional horizontally polarized antenna design includes dipoles arrayed in a quadrature configuration in the same plane and excited in a phase relationship that generates an overall far-field transmission pattern that is a sum of the four dipole transmission patterns. However, the E-plane transmission pattern for a single half-wavelength dipole has a half-power beamwidth of approximately seventy-eight degrees (78°). As a result, the far-field transmission pattern has an approximate three (3) dB loss (e.g., a dip, or a null which is a region of low intensity) every forty-five degrees plus the product of ninety and n-degrees (e.g., 45°+90n°), where n=0, 1, 2, 3 in the omni plane.
Accordingly, there is a need for a high gain antenna that provides an E-plane omni-directional transmission pattern without nulls or losses that preclude complete coverage over a desired transmission region.